Evaporator froze up again.

[kuehl]

Originally Posted by porschedurango

just want to confirm before I overcharge.
95f day today, low pressure between 25-30, hi 200-250

In a perfect world you would want, at idle, 228 psi on the hi.

trunk lid up

NO. Trunk lid down and gently resting on the service set hoses.

big fan on cooler

NO. No additional fans other than those permanently designed for the system (system mean OEM or aftermarket),,,, meaning: don't aim a temporary fan

spray with water to keep it cool

NO. You car does not have a 'spray water' as part of its system. Spraying water on a condenser is done in diagnostic procedure.

center duct inside stays at 60 degrees

No terrific but better than 95F. Vent temps are affected by other factors, such as:
fan speed, compressor speed, vehicle speed, are the windows up or down and a host of other factors

system holds pressure

Time will tell.

[boxster03]

Evaporator? is that a freezer or a Porsche

[Mitch Leland]

Mark,

I've quickly read all the posts, I agree that one of the most important things you can do is to properly insert the capillary tube into the evaporator. Charlie Griffiths told me 3.5". There is also a paste that transfers heat (can't remember the name of the material) that will conduct the temps between the evaporator fins and the capillary tube so the switch gets a better reading. Maybe someone will post that information.

However your temp switch and capillary tube could be bad. I had your same problem, and because your compressor is not turning off that sends up a red flag as one of the possibilities. I would replace the temp switch and capillary tube on general principles... Or at least be sure it's working, but I don't know how to do that...

When I replaced mine it solved about 90% of my freezing problems... I kept chasing the Freon charge, when in fact that was never the problem...

[86 911 Targa]

Originally Posted by mthomas58

Drove from Atlanta to Hilton Head today in 85 degree ambient temps (humidity high). Vent temps rose and airfow declined one hour into the trip (classic freeze up symptoms). Turned A/C off and opened up the windows for about 45 minutes, then turned fan on high and temp setting to lowest setting. All seemed well although compressor never shut off (even at lowest temp setting). Evap apparently iced up again....this time I did not notice a reduction in airflow BUT, after refueling in HH upon arrival (15-20min stop) upon start-up, ice shot out the center vents!

OK, to my point. Evap is orig and has recently been cleaned along with evap box. Thinking I need to upgrade to a modern serpentine evap unit to reduce freeze ups. If i do this, I will add a ProCooler "while im in there".

Seems like the condenser fans I've added have helped get my vent temps down but my old technology evap cannot handle it.

Make sense?

After many years of service, the diaphrams on the temp switches have a tendency to lose flexability and/or contact corrosion.

If you buy a new switch, set the compressor cycle for a 10 degree on/off, and center vent temp not to exceed 38 degrees.

Copy of an Email I sent to another P-Member
who is upgrading his A/C.

Assuming that your evaprator probe is inserted properly,
and you have the correct high/low side numbers, try this.

These were the A/C control settings when I adjusted the
temperature switch on a 70F day while on the freeway
as the A/C system is always calibrated at 2000 rpm's.


On a warmer day there are still five increments on the
temperature switch to increase the center duct cooling
2½F per increment. We had a max of 27F on a 70F day.
And one more fan speed.


Upon installation of your new components, take the car for
a drive with a thermometer at the center duct for a test run.
IR guns are very misleading.


I also installed an LED across the condenser fan terminals
which provides A/C compressor on/off indications.

Temperature switch adjustments:

Open the sliding cover.


Set this for a center duct temperature of 38F.
Too cold will freeze up the evaporator.


Set for a 40F-50F center duct temperature.
A 10F window will, by reducing compressor "on" time,
reduce evaporator freeze-up.


NOTE: Do not use the "low" fan speed,
as the low fan speed does increase the
probability of evaporator freeze-up,
especially in a high ambient/humidity environment.
If the air is too cold, reduce the temp control.

However, on long drives, in a high humidity/temperature environment,
the evaporator may eventually show signs of freeze-up.

This symptom is noted by a reduction of air flow, and humid
air emitted from the ducts.

Increasing the fan speed to maximum,
and reducing the temp control, will increase
air flow and may remove the ice from the evaporator.

All of the above assumes that you have a stock A/C/R12 configuration
with the addition of the two stage Pro-Cooler, and the Rennaire
High flow evaporator.

On a 95F day in Palm Springs, we have 45-50F center duct temperatures on the freeway.

Good luck,

Gerry

[porschedurango]

I have the deck-lid open 1 inch and it's 92 outside. with the car warmed up low side is 43 and high is 385. it starts off blowing cold at 65 then when warmed up it blows cold air at 80 degrees. Just asking if im overcharged and if so should i recycle it out from the low or high side into a tank. if overcharged what pressures should i bring it down to when the engine is warm?

[curiousone940]

My .02 cents worth on this subject. I have switched my entire A/C system over to 134, Sanden compressor, serpentine evap coil, new barrier hoses, new thermostat/exp. valve/dryer and I still have some evap icing issues. System pressures are within specs and as some have previously stated in this thread, I've checked to make sure the thermo capillary tube is set on the coldest part of the evap coil. System pressures can of course cause evap icing, however, I think in my case, there is not enough air flow over the evap coil itself to prevent undue build up of moisture and then ice. Of course, higher humidity weather will only compound the problem. I have found that 1.) I need to carefully monitor vent temps with a digital thermometer (adjust the thermostat where the compressor will cut off at about 42 degrees) and 2.) if/when I see the vent temps going up (an indicator of impending icing), I increase the blower fan to full high and back off (i.e. warm up a bit) on the thermostat until the icing problem ceases, THEN go back to the lower vent temps and medium blower fan.

The way evap coils and the blower fan are designed in these years of P-cars, there is a water wicking problem in the evap coil which in effect holds the water in the coil like a sponge AND there is not sufficient air flow from the blower motor to keep the moisture off of the coil and out the drain tube; if your therno capillary tube is not correctly inserted into the coldest part of the coil, then your are going to have an icing issue. A larger CFM blower motor would help the situation, some of the newer serpentine evap coils are not as prone to wicking; otherwise, about all you can do (if this is your problem) is to monitor vent temps and adjust your blower fan speed and thermostat accordingly.

[El_Mecanico]

Marc is the copper tube really a necessary? I don't want to have to remove the evap. I'm like you monitor the temps and adjust temp switch. Here in lower Alabama is very very humid. Originally I had the capillary tube in the wrong spot. I moved it to the hole on top and pushed it so all the bare metal was inserted. So far no freezing evap.

[El_Mecanico]

Well I just looked at my old evaluate and realized it didn't have a tube but someone did make room in the coils for one. Guess I will make the fix.

[wwest]

Originally Posted by patkeefe

Either low on refrigerant, or not enough airflow over the evaporator. Those are the two most certain causes of icing.

The ONLY possible cause for frozen condensate on/in the evaporator vanes is the lack of A/C compressor control. The A/C compressor clutch control system should ALWAYS open the circuit with sustained vane temperatures of less than ~35F.

You might have other contributing factors/problems but in the end the clutch control system, if working properly, will ALWAYS override those.

[patkeefe]

Thank you for bringing absolute expertise to this board.

[llangston1]

Is there a preferred way to insert the capillary tube into a serpentine evaporator to get the best temperature sensing and prevent ice ups? My car has a Rennaire evap and a PO had just stuck the tube into the core vertically without the protective tube. I suffered several iceups on the trip to and from the Savannah parade. I thought the switch was bad but it seems to work fine in a cup of ice. Should the tube just stick into the core vertically or should I the to insert it at an angle even though that will mean it has to go through several sets of vanes. How mush of the tube needs to be inserted? The last 6" or so of my tube is uninsulated but only the last 3" was in the evap. Should I insulate all of the exposed tube that is not in the core?

[86 911 Targa]

Originally Posted by llangston1

Is there a preferred way to insert the capillary tube into a serpentine evaporator to get the best temperature sensing and prevent ice ups? My car has a Rennaire evap and a PO had just stuck the tube into the core vertically without the protective tube. I suffered several iceups on the trip to and from the Savannah parade. I thought the switch was bad but it seems to work fine in a cup of ice. Should the tube just stick into the core vertically or should I the to insert it at an angle even though that will mean it has to go through several sets of vanes. How mush of the tube needs to be inserted? The last 6" or so of my tube is uninsulated but only the last 3" was in the evap. Should I insulate all of the exposed tube that is not in the core?

You will need to replace the brass tube that is first inserted into the evaporator core, which accepts the capillary tube probe.

pm me as needed.

Gerry

[kuehl]

Originally Posted by llangston1

Is there a preferred way to insert the capillary tube into a serpentine evaporator to get the best temperature sensing and prevent ice ups? My car has a Rennaire evap and a PO had just stuck the tube into the core vertically without the protective tube. I suffered several iceups on the trip to and from the Savannah parade. I thought the switch was bad but it seems to work fine in a cup of ice. Should the tube just stick into the core vertically or should I the to insert it at an angle even though that will mean it has to go through several sets of vanes. How mush of the tube needs to be inserted? The last 6" or so of my tube is uninsulated but only the last 3" was in the evap. Should I insulate all of the exposed tube that is not in the core?

You don't need the brass sleeve to make the capillary sensing tube work. What the brass sleeve does is it provides protection of the aluminum capillary sensing tube to help prevent breakage.
Contact Ron at Rennaire and ask him where to place the sensing tube. If his solution does not work then PM me and I'll walk you through it.

[Mitch Leland]

I would be sure that your sensing tube is making contact with the evaporator fins. If the PO has used the brass sleeve previously and now you're just using the sensing tube, there's a chance that you're shoving the sensing tube into thin air. I would get the brass jacket... I know that Griff furnishes a new one with his evaporators.

Also get some thermal transfer paste that will aid the conductivity between your fins and capillary tube. You can find this material at Radio Shack.

If you were running your A/C when it's humid then that's another reason for evaporator freeze up. Did you back off the temp switch setting and increase the fan setting, that might help prolong the freeze up. It's a common problem...

[86 911 Targa]

The tube also protects the the capilary tube from impacting against the evaporator fins while maintaining a constant location.

It does not take much of a deviation to send the wrong signal to the temperature switch.

The first part of this thread shows how to make one from brass tubing available at most hobby shops.

Porsche had a good reason for including the brass capilary tube holder.

[Mitch Leland]

One thing to remember if you're making up your own brass sleeve is that the one you get from your local Ace Hardware is a SAE dimension. The original sleeve is a Metric which gives you better/tighter contact with the capillary tube.

I would gently squeeze the SAE sleeve to give you better contact with the capillary tube and use the thermal transfer paste.

[Hodgey]

On a 95F day in Palm Springs, we have 45-50F center duct temperatures on the freeway.

Good luck,

Gerry, hope you are keeping well.
45-50 would be superb!!! I get to 60 here in Alabama in 90+degree heat with lots of humidity so I am thrilled...I have started getting evap freezing issues on longer journeys so I'll try running the fan at high speed........and I will check the bras capillary tube at the weekend....

Neil

[Mitch Leland]

FYI... I have a well placed, positive connection w/ my capillary tube at the evaporator fins. I also have Griffith's variable fan switch, Griffith's panel light, Griffith's front condenser and evaporator. Included is a ProCooler which makes up my system.

I just returned from a 2,500 mile road trip and here's what I got... No humidity to speak of:

95 degrees ambient - 43.6 degrees at the vent...
97 degrees ambient - 49.5 degrees at the vent...

I run the fan about 2:00 and the temp switch at about 6:00. If I set the temp switch/dial much lower the compressor won't cycle. I'm not sure why that happens, but with my panel light I can tell when the compressor turns off. If you run the compressor so it won't cycle you're bound to get freeze up sooner or later...

[quattrorunner]

good thread